This invention relates to an air/fuel induction system for a multi-cylinder internal combustion engine and to electronic control apparatus for controlling fuel supply to the engine. In particular it relates to an internal combustion engine having a plurality of fuel supply valves feeding an air/fuel induction passage, wherein the quantity of fuel delivered by said valves at each opening is determined by the period of said opening, and which period is controlled by the width of a fuel pulse signal developed by the electronic control apparatus.
The description filed with the present Applicant's co-pending application Ser. No. 555,481 filed Nov. 28, 1983 relates to a dual fuel system for an internal combustion engine, enabling a driver of a vehicle to select as fuel either petrol or liquefied petroleum gas. The LPG system incorporates a pair of fuel injection valves which are operated alternately. The present invention may be applied to such a system or to other fuel systems in which fuel is delivered into an air/fuel induction passage, prior to the inlet manifold, via a plurality of valves.
Multiple valve, multipoint fuel injection systems are well known. In these systems fuel is injected directly into a cylinder of the engine by a respective injector valve on each cylinder. It has been proposed to allow the operating periods of the injector valves to overlap. For example EP A No. 0034076 discloses a multipoint injection system wherein 6 injector valves are provided, each injecting directly into an associated cylinder of the engine. The disclosed system allows the operation of the two of the injector valves to overlap by a small amount at high engine speeds. It will be appreciated however that during an overlap period when two cylinders are simultaneously being supplied with fuel, this fuel is directed separately and independently into the two cylinders and there is no question of one cylinder receiving fuel designated for another cylinder.
By contrast, the present invention is concerned solely with injection of fuel into an air/fuel induction passage which is common to a plurality of cylinders.
In single valve systems the valve, operating in synchronism with cylinder firings, may be required to operate in a frequency range of 20-200 Hz. Such valves are expensive. In an LPG system the valves are also required to have large outlet orifices; this makes it difficult to operate efficiently at high frequencies, and also tends to cause the fuel to be supplied in undesirable large gusts at low frequencies. Dual or multi-valve systems with alternate operation allow the operating frequency range of individual valves to be smaller.
The valves may still have to have the same capacity as the valve in the single valve system in order to be capable of supplying enough fuel at high engine speeds. Thus the gusting of the fuel at low frequencies will still occur. An object of the present invention is to alleviate these difficulties.
According to the present invention there is provided an air/fuel induction system for a multi-cylinder internal combustion engine comprising an air/fuel induction passage, a driver-operable throttle valve for controlling the flow of air/fuel mixture to cylinders of the engine, fuel injection means operative to deliver metered pulsed outputs of fuel to a location in the induction passage, upstream of the inlet manifold, and electronic control means operative to produce electrical signals to control the duration of each pulse output of fuel from the fuel injection means,
wherein the fuel injection means comprises at least two injector valves operated sequentially under control of said electronic control means, such that the commencement of a pulse output of fuel is synchronised with the operation of the engine, and such that under predetermined engine operating conditions the opening periods of at least two of said valves overlap.
The invention also provides an electronic control apparatus for the air/fuel injection system as aforesaid, the control apparatus being adapted to receive signals representing engine operating parameters, and including signal processing means, which on the basis of the values of said received signals, produces an output signal representing a value for controlling the duration of a pulse output of fuel from the fuel injection means,
the apparatus further including means for feeding pulse width signals representing said output signals sequentially to said injector valves, each pulse width signal being fed independently to an injector valve such that an injector valve may receive a pulse width signal while another injector valve is also receiving a pulse width signal.
In one example the means for feeding pulse width signals representing said output signals comprises independent timers associated with respective injector valves, each timer receiving sequentially a control signal from said signal processing means to determine its timing period and being operative to produce a pulse width signal, whose duration is determined by its timing period, for transmission to control the associated injector valve.